1. Field of the Invention
This invention relates to a printing technique for printing solder to a substrate overlaid on a back surface of a mask by moving the solder by a squeegee on a front surface of the mask.
2. Background Art
Japanese Patent Application Laid-Open No. 2010-064425 describes a printing machine for printing solder to a substrate overlaid on a back surface of a mask by moving the solder with a squeegee on a front surface of the mask. More specifically, this printing machine has the squeegee that slides on the front surface of the mask plate, and when this squeegee moves thereon while scraping the solder, the solder is filled into a pattern hole formed in the mask plate. In this manner, the solder filled into the pattern hole is printed onto the substrate overlaid on the back surface of the mask plate.
By the way, when there is a large amount of solder on the front surface of the mask in such printing machine, the squeegee is unable to sufficiently scrape off the solder from the front surface of the mask, and a layer of remaining solder which was not scraped off may be formed on the front surface of the mask. In such case, the remaining solder which was not scraped off additionally stays on the solder filled into the pattern hole of the mask, and as a result, a large amount of solder is printed on the substrate. On the other hand, there is a small amount of solder on the front surface of the mask, the solder filled into the pattern hole may be scooped out by the squeegee. In other words, the squeegee sliding on the front surface of the mask scrapes the solder and moves thereon while filling the solder into the pattern hole located at the front side in the sliding direction. At this occasion, the squeegee fills the solder into the pattern hole, and thereafter the squeegee passes over the pattern hole. Therefore, when there is a small amount of solder on the front surface of the mask, the solder filled into the pattern hole may be scooped out as the squeegee passes over the pattern hole. In such case, only a small amount of solder is printed onto the substrate. Or, even when such remaining solder which was not scraped off or remaining solder which was not scooped out can be disregarded, the amount of solder printed onto the substrate may change depending on the amount of solder on the front surface of the mask due to some other reasons. In other words, when there is a large amount of solder on the front surface of the mask, the force for filling the solder into the pattern hole increases, and the amount of solder printed on the substrate may increases. On the other hand, when there is a small amount of solder on the front surface of the mask, the force for filling the solder into the pattern hole decreases, and the amount of solder printed on the substrate may decrease. As described above, in the printing machine as described above, the amount of solder printed onto the substrate may become unstable depending on the amount of solder on the front surface of the mask.